Cleaning system using volatile solvents and method of reducing solvent losses therein

ABSTRACT

IN A DRY-CLEANING PLANT A SINGLE PUMP IS USED TO EVACUATE A FRESHLY LOADED TREATMENT DRUM AND, AFTER CLEANING OPERATION, THE EXTRACT SOLVENT VAPORS FROM THAT DRUM. IN THE FIRST PUMPING PHASE, THE AIR IS DISCHARGED INTO THE ATMOSPHERE BY WAY OF A FIRST OIL SEPARATOR WHICH REMOVES ENTRAINED LUBRICANT; IN THE SECOND PUMPING PHASE, THE VAPORS PASS THROUGH A SECOND OIL SEPARATOR INTO A CONDENSER FOR THE RECOVERY OF SPENT SOLVENT. THEREAFTER, THE TWO OIL SEPARATORS ARE EMPTIED INTO A RESERVOIR WHOSE TOP IS CONNECTED WITH THE SUCTION SIDE OF THE PUMP FOR REMOVAL OF RESIDUAL SOLVENT VIA THE SECOND OIL SEPARATOR TO THE CONDENSER; THE REMAINING OIL IS THEN RETURNED TO THE CRANKCASE OF THE PUMP.

Oct. 19, 1971 FUHRlNG ETAL 3,613,135

CLEANING SYSTEM USING VOLATILE SOLVENTS AND METHOD OF REDUCING SOLVENT LOSSES THEREIN Filed March 27, 1970 PROGRAMMER as s5 COND. I v

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United States Patent 3,613,135 CLEANING SYSTEM USING VOLATILE SOLVENTS AND METHOD OF REDUCING SOLVENT LOSSES THEREIN Heinrich Fuhring, Augsburg, and Johannes Helmut Sieber, Aystetten, Germany, assignors to Firma Bowe, Bohler & Weber KG, Augsburg, Germany Filed Mar. 27, 1970, Ser. No. 23,402 Claims priority, application Germany, Mar. 31, 1969, P 19 16 523.2 Int. Cl. D061? 43/08 U.S. Cl. 8-158 12 Claims ABSTRACT OF THE DISCLOSURE In a dry-cleaning plant a single pump is used to evacuate a freshly loaded treatment drum and, after cleaning operation, the extract solvent vapors from that drum. In the first pumping phase, the air is discharged into the at mosphere by way of a first oil separator which removes entrained lubricant; in the second pumping phase, the vapors pass through a second oil separator into a condenser for the recovery of spent solvent. Thereafter, the two oil separators are emptied into a reservoir whose top is connected with the suction side of the pump for removal of residual solvent via the second oil separator to the condenser; the remaining oil is then returned to the crankcase of the pump.

Our present invention relates to a cleaning system in which volatile solvents are used for the removal of soil and grease, eg with the aid of a rotating vessel or tumbler receiving the goods to be treated. Typical of such systems are dry cleaning plants for textile fabrics; another field of application is the degreasing of metallic articles.

In a conventional dry cleaning system, for example, the textiles are loaded into a rotatable drum within a housing adapted to be sealed against the atmosphere; at the beginning of operations, usually with the drum already in rotation, air is evacuated from the housing to create a partial vacuum in the drum and within the interstices of the fabric. A volatile solvent, such as a fluorinated chlorohydrocarbon (e.g. perchloroethylene), is then admitted into the drum and is taken up by the load to react with the soil. After a sufiicient treatment period, the evolving solvent vapors are exhausted with the aid of a pump advantageously directing them into a condenser for subsequent re-use.

In U.S. Pat. No. 3,323,335 there has been disclosed a dry cleaning machine of this type with two cascaded pumps which during the drying phase, i.e. during the ex haustion of the solvent, work into a condenser by way of a still. During the initial evacuation phase, on the other hand, only the first pump is operative to discharge the aspirated air into the atmosphere after passing it through an oil separator to free the air from entrained lubricant. The lubricating oil is then returned to the crankcase of this pump.

With systems of this and similar types, utilizing an oillubricated extraction pump during the drying phase, some solvent is unavoidably admixed with the entrained lubricating oil and returned with it to the crankcase. This solvent is lost to the cleaning process and also impairs the lubricating quality of the oil.

The general object of our present invention, therefore, is to provide a method of and means for so operating such a cleaning system as to avoid the loss of solvent and the contamination of lubricant in the aforedescribed manner.

Another object is to provide a simplified system in 3,613,135 Patented Oct. 19, 1971 which the same pump can be used for both the evacuation and the drying cycle.

These objects are realized, pursuant to one aspect of our invention, by connecting the high-pressure or output side of an extraction pump alternately to a first and a second oil separator, the first oil separator being included in a fluid path for discharging the evacuated air to the atmosphere whereas the second separator lies in another fluid path terminating at a condenser for the extracted solvent vapors. Entrained lubricating oil is thus removed from the solvent-free air during the evacuation phase and from the solvent vapors during the drying phase, the lastmentioned oil being collected exclusively in the second separator which therefore also receives all the residual solvent admixed therewith. At the end of the drying phase, or at some convenient time thereafter, both oil separators are drained concurrently or consecutively into an oil reservoir which is thereafter connected to the low-pressure or suction side of the pump for removal of the solvent residue. The residue is then delivered, advantageously by way of the aforementioned second oil separator, to the condenser for further utilization together with the solvent already accumulated there. The purified oil in the reservoir can now be returned to the pump crankcase which, for this purpose, may be temporarily connected to the suction port of that pump either directly or via the oil reservoir. With the top of the crankcase connected at that time to the top of the reservoir, a circuit is established for pressure equalization and for the exhaustion of any remaining solvent traces from the crankcase to the pump intake and thence to the condenser.

According to another advantageous feature of our invention, the solvent-collecting receptacles of the oil-circulation systemi.e. the second oil separator and the oil reservoirare heated with the aid of a fluid of elevated temperature that may also pass through a still into which liquid solvent from the treatment vessel is drained just before the drying phase. The regenerated solvent from the still can be fed to the condenser by the same pump which extracts the solvent vapors from the vessel.

The above and other features of our invention will be described in greater detail hereinafter with reference to the accompanying drawing in which:

FIG. 1 is an overall diagrammatic view of a treatment plant, specifically a dry cleaning system, embodying the present improvement;

FIG. 2 is a timing diagram illustrating the sequence of operations of the system of FIG. 1; and

FIGS. 3 and 4 are fragmentary diagrammatic views showing modifications of that system.

The system of FIG. 1 includes a machine housing 1 in which a treatment vessel 3, such as a drum of the type conventionally used in dry cleaning establishments, is rotatable by means of a motor not shown. A pump 2 associated with machine 1 has a crankcase 2a with a motordriven crank 2b coupled to a reciprocable piston 20. Conventional check valves, not shown, allow the aspiration of fluid into the piston cylinder at an intake port 2d and the expulsion of that fluid at a discharge port 22. The top of housing 1 is connected with intake port 2d by way of a conduit 4 including a shut-off valve 14; two other conduits 17 and 25, provided with respective shut-off valves 15. and 26, merge with conduit 4 ahead of port 2d.

Discharge port 2e is connected by way of two parallel branch lines 8 and 12, containing respective shut-01f valves 6 and 5, with a first oil separator 7 and a second oil separator 10. An extension conduit 9 leads from oil separator 7 to the atmosphere, a similar conduit 13 extending from oil separator 10 to a condenser 11 fitted with the usual cooling coils not shown. The precipitate actuating in 34-to a-"tank'for"regenerated solvent to be re-usedin Fluid line 17 originates at a still 16 into which liquid solvent from casing 1 may be emptied by way of a conduit '36 containing a shut-off valve 36a. Fluid line 25 starts at the top of an oil reservoir 20 into which the contents of separators 10 and 7 can be drained through respective pipes 28, 29 provided with shut-off valves 18 and 19. A common heating circuit for still 16, reservoir 20 and oil separator 10 comprises a conduit 30 receiving hot oil or other tfluid from a heater (not shown) by way of a supply line 32 and a control valve 32a; another valve 31a is inserted in a bypass .31 which, like line 30, terminates at a storage vessel '37 from which a return line 38 extends to the heater.

From the bottom of reservoir 20 a conduit 21, including a shut-off valve 22, is led to an oil inlet 33 for crankcase 2a which may be provided with level-control means, not shown, for the oil pool in crankcase 2a. A pressureequalizing conduit 23 with shut-off valve 24 extends from the upper of the crankcase, above the oil pool, to the top of reservoir 20.

Drum housing 1 is further provided with a venting valve 27 to re-admit air into the evacuated treatment vessel preparatorily to the opening of its lid for the unloading and reloading of drum 3. A programmer 35 controls the timing of the opening and closure of valves 5, 6, 18, 19, 22, 24, 26, 27 and 36a as well as the energization of the drive motors for drum 3' and pump 2. The first graph of FIG. 2 illustrates the operating periods of pump 2 whereas the remaining graphs w show the open conditions of the valves controlled by the programmer.

As shown in FIG. 2, at the beginning of an operating cycle (during which the drum 3 rotates with a load of garments or the like) all the aforementioned valves are closed and the pump 2 is at standstill. At a time t the pump is set in motion and valves 6 and 14 are opened. Air is now evacuated from housing 1 and drum 3 via conduit 4, ports 2d and 2e, conduit 8, oil separator 7 and conduit 9 so that a partial vacuum is developed in the machine; this vacuum prevents any untimely opening of the machine housing 1. At time t valves 6 and 14 close and pump 2 is arrested (although this is not essential); liquid solvent from a supply tank, which may be replenished from time to time from condenser 11 and other sources, is introduced into housing 1 through an inlet not shown whereupon tumbling of the goods in the drum is continued for a predetermined period at the end of which (as indicated at i the liquid solvent is drained from the drum by the opening of valve 36a. Shortly thereafter, at a time t valves 14 and are opened while pump 2 is restarted to draw solvent vapors from the drum and its housing into port 2d and to discharge them through oil separator into condenser 11. This operation continues up to a time t when, with the opening of valve 27, the interior of housing 1 is vented to the atmosphere while valve 14 is reclosed. At a time t the valve 27 closes whereupon the system is ready for the removal of the previous load and the introduction of a new one into drum 3. At a time t valves 18, 19 and 26 are opened with resulting drainage of oil separators 7 and 10 into reservoir and the exhaustion of solvent fumes from that reservoir into the intake port 2d of the pump 2 whence these fumes are directed through the open valve 5 into oil separator 10 and condenser 11. This condition continues up to a time,

t when valves 18 and 19 are closed to generate the necessary suction in reservoir 20 for the removal of substantially all the entrained solvent. At a time t valves 22 and 24 are opened whereby the suction prevailing in reservoir 20 is communicated to crankcase 2a and the oil accumulated in reservoir 20* is returned to that crankcase, with extraction of any remaining solvent traces by way of lines 23, 25, 12 and 13. Finally, at a time r the pump 4 stops and valves 5, 22, 24 and 26 are closed in for the start of a new cycle (time 13,).

The emptying of oil separators 7 and 10 into reservoir 20 need not be carried out during every cycle; in fact, oil separator 7 may be continuously connected with the reservoir through omission of valve 19 inasmuch as this separator does not contain any volatile components. Valves 22, 24 and 26 could also be omitted in a simplified system.

As illustrated in FIG. 3, conduit 25 may be attached directly to the equalizing line 23 instead of communicating with it through the reservoir 20 as in FIG. 1.

FIG. 4 illustrates the possibility of letting the conduit 25 originate at the crankcase 2a through which it communicates with equalizing line 23. This arrangement is less advantageous than those of the preceding figures since the oil in the reservoir 20, when subjected to the suction of intake port 2d, will tend to foam and will therefore have a reduced lubricating effect. Especially with the arrangement of FIG. 1, the return of foaming oil to the preparation crankcase will be positively prevented; it may be noted in .this connection that the foaming problem precludes the use of the crankcase itself as the oil reservoir.

If, with valve 26 omitted, the reservoir 28 is under constant suction as long as pump 2 is in operation, valve 18 should be closed during the evacuation phase so as to prevent the escape of recirculated solvent. Preferably, this valve should also stop the outflow from oil separator 10 during the drying phase in order not to diminish the efficiency of the pump by the superimposition of an additional fluid flow upon the vapor stream extracted from housing 1. On the other hand, valves 14 and 15 are advantageously closed during solvent recovery from reservoir 20 so that the full suction of pump 2 is available in line 25. The opening of valve 15, not indicated in the diagram of FIG. 2, should of course be timed to coincide with that of valve 36a to assist in the draining of housing 1 during the interval t -t this does not necessarily occur during every cycle.

The timing diagram of FIG. 2 may be modified, for example, by a relative shifting of the various valve-open periods into partly overlapping positions or alternatively, by the introduction of additional intervals therebetween. Thus, for example, the draining of the solvent pool from housing 1 (during period t t may be followed by a prolonged centrifugation period during which the load is mechanically predried before commencement of solvent extraction by the opening of valves 5 and 14.

We claim:

1. In the process of treating a load in a closed vessel with volatile solvent, the loaded vessel being evacuated by an oil-lubricated pump in a first working phase followed by introduction of solvent and subsequent exhaustion of solvent vapors by said pump in a second working phase, the improvement comprising the steps of:

(a) discharging air from said vessel into the atmosphere in said first working phase by way of a first separator for entrained lubricating oil connected to the high-pressure side of said pump;

(b) discharging solvent vapors from said vessel into a condenser in said second working phase by way of a second separator for entrained lubricating oil connected to the high-pressure side of said pump;

(c) transferring the contents of said first and second separators into an oil reservoir; and

(d) connecting the top of said oil reservoir with the low-pressure side of said pump for exhausting residual solvent vapors and directing same to said condenser.

2. The improvement defined in claim 1 wherein, following step (d), the oil in said reservoir is returned to said pump for lubricating same.

3. The improvement defined in claim 2 wherein the pump has a crankcase for said oil, comprising the further step of connecting the top of said crankcase, with the top of said reservoir in a pressure-equalizing circuit at least during the return of the oil.

4. The improvement defined in claim 3 wherein said pressure-equalizing circuit is at least temporarily connected to the low-pressure side of said pump.

5. The improvement defined in claim 1 wherein steps (a) through (d) are periodically repeated with intervening unloading and reloading of said vessel.

6. The improvement defined in claim 1 wherein said second separator and said reservoir are heated at least during steps (b) through (d).

7. A system for the treatment of a load with volatile solvent, comprising:

a closable vessel for a load to be treated;

an oil-lubricated pump having a low-pressure side connectable to said vessel for extracting fluids therefrom and further having a high-pressure side for the discharge of such fluids;

a first fluid path leading from said high-pressure side to the atmosphere;

a first oil separator in said first fluid path;

a condenser for vaporized solvent;

a second fluid path leading from said high-pressure side to said condenser;

valve means for selectively opening and closing said first and second fluid paths;

an oil reservoir connectable to said oil separators for receiving their contents; and

conduit means for establishing an exhaust connection for residual solvent between the top of said reservoir and said low-pressure side.

8. A system as defined in claim 7 wherein said pump is provided with a crankcase, further comprising a return path for delivering oil from said reservoir to said crankcase.

9. A system as defined in claim 8, further comprising a pressure-equalizing circuit extending between the top of said crankcase and the top of said reservoir.

10. A system as defined in claim 9 wherein said pressure-equalizing circuit is provided with an extension leading to said low-pressure side.

11. A system as defined in claim 7 wherein said second 3 oil separator and said reservoir are provided with heating means.

12. A system as defined in claim 10, further including a still for solvent removed from said vessel connected to said condenser via said pump and said second fluid path, said heating means being operatively connected with said still.

References Cited UNITED STATES PATENTS 3,323,335 6/1967 Schneider 68-18 R WILLIAM 1. PRICE, Primary Examiner US. Cl. X.R. 

